Screw compressor control means

Claim 1

In a screw compressor comprising a casing with a working space disposed therein in the shape of two intersecting cylindrical bores with parallel axes, a high pressure end wall at one end thereof, a low pressure end wall at the other end thereof, intermeshing male and female rotors disposed in said working space in sealing engagement with said casing and the end walls thereof and having helical lands and intervening grooves with a wrap angle of less than 360°, said male rotor having the major portion of its lands and grooves outside the pitch circle thereof and with its flanks substantially convex, and said female rotor having the major portion of its lands and grooves inside the pitch circle thereof and with its flanks substantially concave, a low pressure port adjacent said low pressure end wall, a high pressure port at the end of said working space opposite from said low pressure port and with said ports being located substantially on opposite sides of a plane through the axes of said bores, an inlet channel in said casing in flow communication with said low pressure port and an outlet channel in said casing in flow communication with said high pressure port, means for varying the volumetric capacity of the screw compressor, comprising: at least one valve bore parallel to the axes of the rotors and disposed on the high pressure side of said plane through the axes of the rotor bores; a plurality of axially spaced overflow channels in said casing and in communication with the working space; an axially adjustable valve body disposed in said at least one valve bore and sealingly cooperating with the barrel walls of the at least one valve bore to divide said valve bore into two valve chambers; one of said valve chambers of said at least one valve bore being completely out of communication with the outlet channel of the compressor and in flow communication with the working space through said axially spaced overflow channels and being further in communication with a low pressure channel, the other of said valve chambers being selectively in communication with a pressure liquid source; and means for axially adjusting the position of said valve body so as to selectively block said overflow channels for variation of the communication between the working space and the at least one valve bore through said overflor channels.